Ductal carcinoma in situ (DCIS) is a relatively common diagnosis among women undergoing screening mammography. The greatest increases in DCIS incidence have been in non-comedo subtypes of DCIS that are not associated with subsequent invasive cancer. After a 500% increase in DCIS from 1983 to 2003, the incidence of DCIS declined in women aged 50 years and older, whereas the incidence in women younger than age 50 continues to increase. Having undergone mammography is one of the strongest and most prevalent risk factors associated with a diagnosis of DCIS. Other risk factors for DCIS are similar to that for invasive cancer including increasing age, family history of breast cancer, high mammographic breast density, and postmenopausal hormone therapy use. Treatment for DCIS is relatively aggressive with the use of both surgery and radiation therapy and most recently adjuvant hormonal therapy. Breast cancer mortality is low and similar with all types of treatment. New information regarding incidence of DCIS and subtypes of DCIS according to frequency of mammography and risk factors could lead to insights into the biology of DCIS.